The following discussion of the background to the invention is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known, or part of the common general knowledge (in any country) as at the priority date of any of the claims. Furthermore, much of the following description is provided with the production of paper or a paper-based product as the context. This is done for ease of description and is not to be regarded as limiting in relation to final uses for the fibre furnish.
Herbaceous plants have been relied upon as a feedstock for paper for thousands of years. However, for at least the last century, wood has become the primary fibre source for paper feedstock, and pulping has become by far the major fibre processing technique. Indeed, the demand for pulp over that period of time has given rise to several of the world's more prominent and controversial environmental and ecological issues.
It is accepted that the conversion of wood into paper requires the use of heavy-duty industrial processes, typically requiring very large energy inputs, high volumes of process water, and having high waste levels, and generally using chemicals that give rise to difficult and sometimes hazardous disposal and recycling requirements. Also, the pulping process, be it chemical or mechanical, is often unable to adequately control the condition and geometry of fibres in the furnish produced, at least to the extent that downstream papermaking processes regard as desirable.
Thus, there has been a growing interest in developing alternative fibre crops for use in the production of paper, and alternative technologies to replace pulping. One source of fibre that has been recognised as a suitable alternative to wood is the banana plant.
The banana plant is a large perennial herb with tall aerial shoots that arise from swollen, fleshy corms (an underground rhizome). The banana plant's petioles are arranged spirally in the aerial shoots, and their long overlapping pulvini (basal enlargements) form the outer portion of a stout, trunk-like pseudostem, through the centre of which the terminal inflorescence grows, forming an inner portion often referred to as a core. Higher up, the petioles bend away from the pseudostem and bear large oval blades (leaves) at an oblique angle.
Each pseudostem can grow to heights normally in the range of 3 to 8 meters over a 9 to 18 month period. When mature, each pseudostem will thus comprise a soft but dense core, surrounded by an outer portion that is tougher but is less dense.
Commercially planted banana plants typically only have 1 to 2 year life-spans, as banana plants only flower (and produce bananas) once, following which the leaves and pseudostem start to die. This usually requires their removal in some manner, such as by simply being cut down, allowing regrowth of a new pseudostem from the rhizome and the commencement of a new reproductive phase.
With annual production in 2002 of about 68 million tonnes of bananas (more than two thirds coming from within India, Brazil, China, Ecuador and the Philippines), it has been recognised that banana pseudostems represent a potentially valuable renewable resource, one which has been traditionally under-utilised and historically economically ignored by banana growers. With this in mind, there have been numerous attempts to use the pseudostems for the production of paper, due to the beneficial properties and qualities of the fibre in the pseudostems.
However, in a paper titled “Banana Stem Fibre for Papermaking” by S. K. Singhai, J. K. Garg and B. Biswas for the Indian Pulp and Paper Journal, August-September 1975, 30(2), pp 13 to 15, the situation at that time was summarised as “The pulping and papermaking qualities of banana (M. sapientum and M. paradisica) stem fibre have been examined. From the available information given in this paper, it is to be considered that neither technically nor economically the use of banana stem fibre is a feasible proposition.” Thus, at least in the mid 70's, no sensible approach had yet been developed for the use of these materials for paper production.
Since then, it has continued to be recognised that banana pseudostem fibres should have suitable properties for paper production. In a paper titled “Plantain (M. Paradisiaca L) Pseudostem; A Fibre Source For Tropical Countries” by Nicholas A Darkwa of the Forestry Research Institute of Ghana, published in Book 2, TAPPI Proceedings, 1998 for the 1998 Pulping Conference in Montreal Quebec, it was concluded that “ . . . tropical countries that are deficient in long-fibred material for their pulp and paper production can utilise the pseudostems of plantain and banana for such purposes.”
Indeed, several attempts have been made to use banana plant refuse (predominantly pseudostems, which includes petioles and cores, and also leaves, immature inflorescence and unused bananas) in existing or modified paper pulping processes—see U.S. Pat. No. 5,958,182 for a short summary of some such processes.
However, such refuse commonly has an extremely high water and natural latex content, and includes numerous resinous and gummy substances that are difficult to handle and process. In order to produce workable fibres having desirable characteristics for paper-making, it has proven necessary to extract these fluids and, in particular, wash out the latex and other natural resinous substances. This has proven to be technically difficult, and has generally made the pulping of banana refuse for the production of paper uneconomic, particularly for bulk paper supplies and for anything other than boutique or artistic papers. It has also generally presented the manufacturers with significant chemical waste disposal issues.
In Australia, while it has been reported that a good quality paper can be made in low volume by combining and pulping banana fibre and betel nut husk (Areca catechu L.), Australian investigators have nonetheless concluded that the yield of banana fibre is too low for extraction in pulping processes to be economical. Indeed, in one Australian report, it was reported that only 1 to 4 oz (28-113 g) of suitable fibre could be obtained from 40 to 80 lbs (18-36 kg) of green pseudostems from a pulping process. Thus, 132 tonnes of green pseudostems would yield only 1 tonne of paper. The conclusion was thus that the pseudostem would have much greater value as organic matter chopped and left in the field to fertilise subsequent crops, which indeed is where the Australian banana growing industry finds itself today.
There have also been suggestions for the use of banana plants without pulping, such as the processes described in International patent publication WO2006/029469 (in the name of Papyrus Australia Limited) and in U.S. Pat. No. 1,981,883 (to Charles O Tappan). The processes described in both documents aim to avoid the pulping problem by providing sheets of fibres directly from the pseudostems of banana plants, with sheets subsequently being used in, for example, laminating processes.
The present invention seeks to provide a further alternative to the use of wood in traditional pulping processes and to provide an improved fibre furnish.